After three impressive showings in leading the Knicks summer league team to a 3-0 record, 7-foot-3 rookie Kristaps Porzingis finally laid an egg along with the rest of his mates as the Knicks were routed by Golden State, 76-54, at Thomas & Mack Center in the opening playoff round.

Porzingis, the fourth-overall pick, made his first 3-pointer of the summer league to start the game but then missed seven straight shots on the way to a 3-of-10, 12-point, four-rebound showing in his summer league-high 24 minutes.

Porzingis also wasn’t as active defensively, blocking just one shot, and admitted afterward he “looked tired.’’

Yes, the 19-year-old Lativan admitted the strain of four games in six days played a factor.

“For me, it’s something new,’’ Porzingis said. “I had almost two games a week [in Spain] the first part of the season. The second part of the season only one game a week and had time to recover. But that’s not an excuse. That’s how the NBA schedule is. I’ve got to get used to it. I’m young. I don’t think it’ll be a problem. I just have to prepare for it mentally, be ready to go out every night and compete and have the same energy for the game.”

Porzingis’ ability to withstand an 82-game grind is definitely an issue as he goes into this rookie season because of his slight frame. In fact, Knicks coach Derek Fisher said the club is debating whether to shut him down for the consolation game/summer league finale Friday.

“We’ll see,’’ Fisher said. “There haven’t been setbacks in terms of an injury. I don’t know if it’s worth the risk.’’

Thursday’s outing is just the reality check that he is 19. In the previous game, Porzingis looked like a shot-blocking extraordinaire, rejecting Philadelphia rookie Jahlil Okafor three times.

“He’s unbelievable,’’ an NBA scout said Thursday night. “Look at the tape of Dirk Nowitzki as a rookie. He’s way ahead.’’

The Knicks shot a pitiful 21.7 percent, scoring just 21 points by halftime, and Fisher said he was disappointed by the low energy level. Cleanthony Early, last year’s prized draft pick, was 0-for-4 with four points and five fouls and rookie point guard Jerian Grant shot just 4-of-12.

“I think you can tell,’’ Porzingis said of the lower energy level. “We started off good, but they started to play with more energy than us and took over the game. We didn’t have a lot of energy. Guys looked tired. I looked tired.”

In his first three outings, the Latvian sharpshooter was so solid and tough on both ends, emerging as a legit shot blocker, it looked like the Knicks might be able to field a starting frontcourt of Porzingis, Robin Lopez and Carmelo Anthony. But Thursday was sobering. Maybe Porzingis’ rookie role will be as a 15-minutes-a-night bench player. The starting power forward spot is up for grabs and the Knicks do not want it to be Anthony, preferring him at small forward.

Asked if he projects Porzingis as his starting power forward, Fisher demurred.

“I wouldn’t judge anybody based on summer league if he’s starting or not,’’ Fisher said. “We’ll have plenty of time to come up with the best lineups to start as well as come off bench. It’s a really long way away. Training camp and preseason will impact that. Kristaps hasn’t really played against the type of guys he’ll play against during the regular season. There isn’t anything he hasn’t done [here] that doesn’t bode well for him going forward.’’

Ironically, Porzingis hasn’t displayed the deadly deep jumper that had scouts drooling during his pre-draft Vegas workout last month. Part of that reason is Fisher has played him at center to get him accustomed to the inside.

“Maybe I’ve surprised some people,’’ Porzingis said. “I still haven’t adjusted 100 percent to the game here, but once I adjust, I’ll feel even more comfortable and play even better.’’

Surprisingly, Porzingis didn’t sink his first 3-point shot until the fourth game of the summer league. But he is drawing a lot of fouls (4-of-5 on free throws Thursday) and drew four defenders after he got a pass in the lane in the first half. He also made an interception at halfcourt and soared in for a breakaway dunk late in the game — stuff 7-3 guys don’t do.

“Some of those shots were not good shots, kind of last seconds on the shot clock, not in a good position to shoot it,” he said. “Some of those didn’t go in. You can’t make every shot.’’

The best big man on the floor Thursday was Golden State’s James McAdoo, who scored 16 points with nine rebounds. Porzingis is averaging just three rebounds.

“He complements guys because of his length and rim protection,’’ Fisher said. “Offensively, his ability to stretch the floor and do things around basket. He’s a player that he fits with any lineup no matter how you try to play. That versatility has been obvious in the summer league.’’

Russian guard Alexey Shved, as expected, signed a three-year, $10.3 million deal with a team in Moscow as the Knicks refused to offer him the $2.8 million exception in a multi-year deal. … Undrafted power forward Maurice Ndour came back to earth with a four-point, six-rebound outing, going 2-of-8 from the field. … The Knicks bench shot 1-of-20 with Ricky Ledo going 1-of-5 and 2014 second-rounder Thanasis Antetokounmpo 0-for-5.